A persistent problem associated with coiled tape measuring rules of conventional construction arises from the entry of dirt into the housing. The dirt tends to produce excessive wear upon the blade faces, and to generally diminish the functional quality of the rule. To a large extent, the problem is attributable to the fact that the blade has an inherent tendency to carry foreign matter into the housing during its retraction.
Proposals have been made in the past for preventing dirt from being introduced into a rule casing in this manner, such as by providing small brush-like components near the opening through which the blade passes, as in Anderson U.S. Pat. No. 3,255,531. It is believed, however, that the arrangement proposed would be of limited effectiveness, and that manufacture of a rule having the feature described in the patent would not be practical on a commercial basis.
Accordingly, it is a primary object of the present invention to provide a novel housing for a coilable measuring rule, and a novel measuring rule employing such a housing, which has means for permitting particulate matter to exit from the housing, so as to thereby reduce resultant wear and functional problems.
A more specific object of the invention is to provide such a housing and rule wherein the means provided for the exit of dirt is very simple and yet highly effective, and also adds virtually no cost or complexity to the manufacturing operations, making the housing and rule most practical to produce on a commercial basis.